A histogram is a graph that shows the overall tonal range of an image — the distribution of tones, from the darkest to the brightest. The histogram is one of the more important concepts in digital photography and understanding it will help you edit your images and use the tools in Pixelmator Pro more confidently.
This is a histogram. The shadow areas in the image are in the left third of the graph, the gray areas are in the middle third, and the highlights are in the right third. Pure black is at the far left edge and pure white is at the far right edge. The higher the graph, the more of the tone is present in the image.
It’s important to keep in mind that there’s no ideal or perfect histogram. It simply graphs the tones of an image, from darkest to brightest. Therefore, a nighttime photo with dark subjects will have a histogram concentrated on the left side, while a bright, sunlit image will have one concentrated on the right side.
However, if a histogram has peaks on the very right or very left edges, it shows the photo contains pure white or pure black areas. If parts of an image are pure black or pure white, it generally means any textures or detail in shadow or highlight areas are not visible. This is often called clipped or blown out shadows and highlights, which is generally not a pleasing look.
Certain color adjustments, for example Levels and Curves, include histograms as part of the adjustment.
In the Levels adjustment, the histogram plays a key role because each slider corresponds to a part of the image displayed in the histogram. The black point slider on the left is located where pure black is on the histogram and in the image. If an image is a little overexposed and has shadows that are a little too bright, moving the current black point will make the shadows darker and redistribute the other tones in the image to make them darker as well. The white point slider is located where white is on the histogram and in the image. Moving it will set a new white point and redistribute the rest of the tones in the image to make everything brighter
The histogram has other uses and there are other histograms in Pixelmator Pro, but understanding the tones of images and how they can displayed in a histogram is a great starting point to expanding your image editing knowledge.